The present invention relates to a method of splicing optical fibers, and more particularly, to a method of reinforcing and protecting a fusion splice between two optical fibers coated with a metal while reducing the size of the reinforced region.
Optical fiber communications systems, and particularly long-distance communications networks, utilize numerous individual optical fibers that must be spliced together end-to-end to provide complete data paths for optical data signals. Such splices must meet two essential criteria: first, they must not unacceptably degrade the quality of transmitted signals, and second, they must not unacceptably weaken the fiber structure. Fusion splicing between glass fibers has seen considerable acceptance as a practical method to achieve the first criterion, and various approaches have adequately addressed the fiber strength criterion for typical fiber applications.
U.S. Pat. Nos. 4,109,369 of Methods of Jointing Optical Fibres issued to Taylor and 4,254,865 of Protective Package for an Optical Fiber Splice issued to Pacey et al. provide examples of one of these approaches. The first shows a system in which the fiber ends are placed in fiber-shaped groove formed in a non-resilient metal plate and secured there by a second plate clamped to the first plate. In the second, a reinforcement article composed of two plastic plate-like halves is secured around the splice area by a layer of adhesive between the halves. U.S. Pat. No. 4,863,234 of Protective Sheath for Optical Waveguide Splice issued to Gladenbeck et al., on the other hand, shows a popular method using a heat-shrinkable plastic tube collapsed about the fiber in the area of the splice. U.S. Pat. No. 4,537,468 of Reinforced Optical Fiber Butt Weld Connection issued to Degoix et al. discloses a third approach using a metal capillary tube, positioned around the desheathed ends of the spliced fibers at the site of the splice, and a particular type of adhesive disposed in the space between the tube and the desheathed fiber ends.
These and similar splice reinforcement techniques provide an acceptable range of solutions for protection and reinforcement of fiber splices in many contexts, but they all have certain limitations that have made them unsuitable for some applications. In particular, some application environments subject optical fibers as a matter of course to unusually harsh conditions such as extremes of temperature, humidity, and mechanical stress. Metal-coated optical fibers have proven to withstand such environments successfully in long-term use, but they present special problems for meeting the two criteria mentioned above for splice protection.
In general, an optical fiber coated with a metal has a significantly greater tension-resistant strength in comparison to optical fibers with polymer sheaths. Metal-coated fibers are also highly resistant to damage from fine bends and from winding. When a metal-coated optical fiber is fusion-spliced, however, it has been difficult to maintain adequately the overall tensile strength of the fiber through previously known methods for reinforcement of the splice. Moreover, adequate reinforcement from a plastic or tubular metal article can easily require the article to have an inconveniently large length dimension relative to bending radiuses frequently encountered in field applications. This large length dimension prevents the spliced area of the fiber from being installed around tight bends, which of course largely nullifies a metal-coated optical fiber's advantage of resistance to bending damage.
I have therefore found that a need exists for a method and article for reinforcing and protecting metal-coated optical fibers while overcoming the limitations of existing approaches using polymers or other materials for reinforcement. Such an invention will substantially preserve the tensile strength of the unspliced metal-coated optical fiber, will do so without sacrificing the metal-coated fiber's ability to undergo tight bends and winding without damage, and will not reduce the spliced fiber's resistance to harsh environments. Preferably the invention will be capable of being carried out in a variety of contexts, including field installation. Ideally, it could be carried out using simple procedures and inexpensive, easily fabricated materials.